The present invention relates to retraction mechanism for emergency locking safety belt retractors and more specifically to retraction mechanisms capable of selectively applying either of two different magnitudes of reel rewind bias to the safety belt retractor reel in response to rotational movement of the reel normally encountered during use of safety belt and harness straps employed with such retractors for holding vehicle occupants in their seats during emergency conditions.
Various types of dual tension safety belt retractor mechanisms have been employed heretofore for selectively applying a main spring rewind bias to the safety belt reel during normal belt protraction and retraction relative to the retractor and for applying a lower tension to the belt while the seat belt is in use about a vehicle occupant user. As is presently known, it is desirable to reduce the tension in a chest belt of a safety harness for automotive passenger restraint when the belt is in use with an emergency locking type of retractor wherein the belt is prevented from protraction, reel unwinding movement, only when an emergency condition occurs. Since the belt is not prevented from an unwinding movement during normal wearing conditions, it is preferred that a rewind bias be continuously applied to the retractor reel in order to prevent buildup of slackness in the safety belt relative to the vehicle occupant employing such safety belt. Moreover, as is also known in the art, it is preferred that when the belt is in use, such rewind bias to prevent slackness in the belt be of a lower value than that normally applied for rewinding the belt onto the retractor reel when the belt is taken out of use. Exemplary of such prior art dual tension retraction mechanisms are those disclosed in copending applications of Charles J. Ulrich, Ser. No. 706,772, filed July 19, 1976, entitled, "Safety Belt Retractor with Dual Tension Retraction Means," the application of Akira Tanaka and Charles Ulrich, Ser. No. 751,753, filed Dec. 17, 1976 now U.S. Pat. No. 4,081,153 entitled "Safety Belt Tensioning and Rewinding Retractor," the application of Akira Tanaka, Ser. No. 701,504, filed July 1, 1976 and entitled "Safety Belt Retractor with Conjugate Return Spring Means," and application of Akira Tanaka, Ser. No. 773,356, filed Oct. 18, 1976 and entitled "Friction Clutch Operated Dual Tension Safety Retraction Means," each of said applications being assigned to the assignee of the within application. While these earlier versions of dual tension retractors are believed to be commercially practicable and satisfactory solutions to a dual tensioning mechanism for emergency locking safety belt retractors, it has been recognized that it would be desirable to design a more simply operable retractor capable of being manufactured at a lower cost and being of a lesser bulk than earlier versions.